Process of making flame retardant cellulosic man-made fibers

ABSTRACT

The invention relates to flame-retardant cellulosic man-made fibers containing a flame-retardant substance in the form of an oxidized condensate of a tetrakis hydroxyalkyl phosphonium salt with ammonia and/or a nitrogenous compound which contains one or several amine groups whereby the fiber has a tenacity of more than 18 cN/tex in a conditioned state. Production process and the use of the fibers according to the invention are further objects of the invention.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to cellulosic man-made fibers with permanentlyflame-retardant properties whereby the flame-retardant property isarrived at by adding an oxidized condensate of tetrakis hydroxyalkylphosphonium salt with ammonia and/or a compound containing nitrogenwhich contains one or several amine groups, to the spinning mass and/orthe spinning solution and the fiber reveals a strength (tensilestrength) in the conditioned state of more than 18 cN/tex.

Description of the Related Art

The cellulosic man-made fibers can be viscose/modal, cupro, or lyocellfibers. Lyocell fibers are defined by BISFA (The International Bureaufor the Standardization of Man-made Fibers) as cellulosic man-madefibers which are spun from an organic solvent without the derivatisationof the cellulose (the direct spinning process). This also means fiberswhich are spun from solutions of cellulose in ionic liquids.

An overview of the methods used to render cellulosic textilesflame-retardant and the mechanisms used for this is supplied by thepublication: Horrocks, A. R.; Kandola, B. K. “Flame Retardant CellulosicTextiles” Spec. Publ.—Royal Society of Chemistry, volume 224, year 1998,pages 343-362. The methods described differ in the element responsiblefor the flame-retardation (mainly phosphorus, however, nitrogen, boronand sulphur as well), the place of the application (surface treatmentmainly with cotton, additive in fiber production with man-made fibers)and the permanency (degree of resistance of flame-retardant propertiesto laundering treatments).

A large share of the permanently flame-retardant cellulosic textiles isproduced by finishing cotton fabrics with tetrakis(hydroxymethyl)phosphonium derivatives (e.g. Proban® finish)respectively with N-methylol dialkylphosphonopropionamides (e.g.Pyrovatex CP®). The finished textiles do, however, have a very hardhand.

Among the cellulosic man-made fibers, a large number of substances weresuggested as flame-retardant additives for viscose fibers in fiberproduction.

In U.S. Pat. No. 3,266,918 Tris(2,3-bromopropyl)phosphate is suggestedas the flame-retardant agent. A fiber of this kind was produced for sometime on an industrial scale. Production was, however, discontinued dueto the toxicity of the flame-retardant agent.

A class of substances used as a flame-retardant agent is that ofsubstituted phosphazenes. A flame-retardant viscose fiber was producedat industrial level on the basis of these substances (U.S. Pat. No.3,455,713). The flame-retardant agent is however in liquid form and canonly be spun into viscose fibers with a lower yield (approx. 75 weightpercent) and it tends to migrate out of the fiber thus giving the fiberan undesirable stickiness.

Similar compounds were described in patents but were never tried forviscose fibers on an industrial scale (BP 1,521,404; U.S. Pat. No.2,909,446, U.S. Pat. No. 3,986,882; JP 50046920; DE 2,429,254; GB1,464,545; U.S. Pat. No. 3,985,834; U.S. Pat. No. 4,083,833; U.S. Pat.No. 4,040,843; U.S. Pat. No. 4,111,701; U.S. Pat. No. 3,990,900; U.S.Pat. No. 3,994,996; U.S. Pat. No. 3,845,167; U.S. Pat. No. 3,532,526;U.S. Pat. No. 3,505,087; U.S. Pat. No. 3,957,927). All of thesesubstances are in liquid form and demonstrate the same disadvantages asin U.S. Pat. No. 3,455,713.

Apart from the above named Tris(2,3-bromopropyl)phosphate, a series ofother organophosphates respectively phosphonic acid amides and esterswere described as flame-retardant agents for viscose fibers (DE2,451,802; DE 2,622,569; U.S. Pat. No. 4,193,805; U.S. Pat. No.4,242,138; JP 51-136914; DE 4,128,638).

Of this class of substances, until now only the compound2,2′-oxybis[5,5-dimethyl-1,3,2-dioxaphosphorinane]2,2 fulfils therequirements with regard to the effectiveness (the necessary amount ofincorporation in order to fulfil EN ISO 15025:2002), quantitative yieldin the spinning process and halogen free.

Apart from the phosphorus compounds mentioned above, flame-retardantviscose fibers were described which contain silicic acid (EP 619,848; EP1,753,900; EP 1,918,431). These fibers pass the flame test describedabove, however, only with high contents of silicic acid. Due to the highcontent of pigment which does not contribute to the tenacity, the fibersdo not attain the necessary fiber tenacities required for textileapplications.

In a series of patent applications, ways were described to impartflame-retardant properties to cellulosic fibers, which are producedaccording to the amine oxide-process. WO 93/12173 describes triazinecompounds containing phosphorus as a flame-retardant agent for plasticmaterials, in particular polyurethane foam. Cellulose is mentioned inclaim 18, spun from a solution in a tertiary amine oxide, without citingan example with regard to the actual suitability of the compounds asflame-retardant agents for cellulose.

WO 94/26962 describes the addition of a tetrakis hydroxymethylphosphonium chloride (THPC)—urea—pre-condensate to the wet fiber priorto drying, ammonia-treatment, condensation, oxidation and drying after asecond washing step. However, condensation reactions at fiber levelsignificantly impair the fiber properties (embrittlement).

In WO 96/05356, lyocell fibers are treated with phosphoric acid and ureaand kept at 150° C. for 45 minutes. This process also damages themechanical properties of the fibers to a considerable extent.

EP 0 836 634 describes the incorporation of compounds containingphosphorus as flame-retardant agents for regenerated cellulose fibers,particularly lyocell fibers.1,4-diisobutyl-2,3,5,6-tetrahydroxy-1,4-dioxophosphorinane is cited asan example. The process has the disadvantage that the incorporationyield of the flame-retardant agent only equals 90% and thus problemsoccur in the closed solvent loops involved in the lyocell process.

U.S. Pat. No. 6,893,492 and WO 2007/022552 describe clay minerals(montmorillonite and/or hectorite) as an additive for lyocell fibers.The flame-retardant effect of these additives does not, however, sufficefor textile products, which have to pass the vertical flame test,according to EN ISO 15025:2002 process B—edge flaming.

In the Korean patent application, Kongkae Taeho Kongbo 2009/025979, aflame-retardant agent containing phosphorus is bonded to the cellulosevia a silicon-oxygen group. This bond is, however, sensitive tohydrolysis and so the product is not suitable for washables.

None of the methods described for the lyocell process has becomeimportant in technical terms. One important reason for this is that theclosed solvent loops in this process place special demands on the yieldwhen incorporating a solid or liquid additive in the spinning mass. Therecovery of solvent equals more than 99%. Even small amounts ofimpurities which get into the spinning bath/washing water build up inthe closed solvent loops as a result of the non quantitative yield ofincorporation and lead to problems when spinning and whenreprocessing/cleaning the solvent.

No patent applications have been announced to date for flame-retardantlyocell fibers, made from ionic liquids (“ionic liquids”). Likewise nopatent applications are known for fibers according to the cupro orcarbamate process. According to BISFA, cupro fibers are a separate fibergenre. In the following, fibers according to the carbamate process arecalled carbamate fibers.

The use of tetrakis hydroxymethyl phosphonium chloride(THPC)—urea—pre-condensates for the flame-retardant finishing of inparticular cotton, involving the process steps impregnation with theprecondensate—treatment with ammonia—condensation—oxidation (e.g. theProban®—process), is known.

The use of fully condensed products is described in U.S. Pat. No.3,645,936. According to the teaching of the patent, the incorporation ofan ammonia/tetrakis hydroxymethyl phosphonium chloride-polymer(THPC/NH₃-polymer) solely with the amount of incorporation which isrequired to pass the flame test (20%), leads to fibers of insufficienttenacity (1.08 g/den=approx. 9.7 cN/tex).

SUMMARY OF THE INVENTION

Surprisingly it has been found that flame-retardant cellulosic man-madefibers possessing a higher tenacity can be obtained by applying aflame-retardant substance as a flame-retardant agent, which is based ona class of compounds known from U.S. Pat. No. 3,645,936.

DETAILED DESCRIPTION OF THE INVENTION

The flame-retardant cellulosic man-made fibers in accordance with theinvention contain a flame-retardant substance in the form of an oxidizedcondensate from a tetrakis hydroxyalkyl phosphonium salt with ammoniaand/or a nitrogen-rich compound which contains one or several aminegroups, and are characterized in that the fiber reveals a strength ofmore than 18 cN/tex in the conditioned state.

The nitrogenous compound is preferably urea or ammonia.

The flame-retardant cellulosic man-made fibers in accordance with theinvention can be viscose fibers or modal fibers. Other fibers accordingto the invention can be produced using the cupro or carbamate process.

The production of viscose and modal fibers is generally known. In thisrespect the addition of functional additives is generally performed bymeans of adding an aqueous dispersion to the spinning mass (viscose).

A process which involves the following steps is particularly well suited

-   -   production of a viscose from cellulose xanthogenate    -   by adding a modification agent    -   addition of 5 weight percent up to 50 weight percent in relation        to the cellulose of the flame-retardant substance in the form of        an aqueous dispersion of the pigment    -   spinning of the spinning mass though a spinneret into the spin        bath    -   stretching of the precipitated filaments    -   after-treatment after washing, bleaching, finishing    -   cutting to staple fibers,

and is characterized in that for the production of fiber

-   -   the pulp used has an R-18 content of 93-98%    -   the cellulose content of the viscose lies between 4 weight        percent and 7 weight percent    -   the alkali ratio lies between 0.7 and 1.5    -   the carbon disulphide input equals 36 weight percent to 42        weight percent in relation to the cellulose    -   between 1 weight percent and 5 weight percent of a modification        agent is added in relation to the cellulose    -   the spinning gamma value of the viscose lies between 50 and 68,        preferably between 55 and 58    -   the spinning viscosity equals 50 to 120 falling ball seconds    -   the temperature of the spinning bath equals 34° C. to 48° C.    -   the following spinning bath concentrations are used        -   H₂SO₄ 68-90 g/l        -   Na₂SO₄ 90-160 g/l        -   ZnSO₄ 30-65 g/l    -   the final drawing off from the spinning bath is performed at a        speed of between 15 and 60 m/min.

Another flame-retardant cellulosic man-made fiber in accordance with theinvention is a lyocell fiber which is produced using a direct spinningprocess, wherein the direct solvent for the cellulose is preferably atertiary amine oxide. N-methyl morpholine oxide (NMMO), which is alreadybeing used at commercial level, is particularly well suited as a directsolvent.

Likewise ionic liquids, such as those known from DE102005062608, can beused as a direct solvent for cellulose.

The production of lyocell fibers according to the amine oxide process isperformed in the following steps:

-   -   1) Contacting the disintegrated pulp with an aqueous N-methyl        morpholine oxide (NMMO) solution.    -   2) Evaporation of excess quantity of water when shearing until a        fiber-free spinning mass has formed.    -   3) Extrusion of the spinning mass through spinnerets, stretching        in an air gap, precipitation of the cellulose in an aqueous        spinning bath containing NMMO, washing and drying.

As an alternative, the production of the spinning mass can also beperformed via the direct dissolution of the pulp in NMMO, containingapprox. 13% water (NMMO monohydrate) in e.g. an extruder.

The addition of the flame-retardant agent can be performed in powderform or as a dispersion in water or in aqueous NMMO in step 1.

The flame-retardant agent can also be added to the spinning mass in theform of a dispersion in NMMO, whereby the NMMO has a water content ofbetween 13 weight percent and 20 weight percent.

As an alternative, the flame-retardant agent can be added in powder formin an extruder.

The average particle size of the flame-retardant agent should be clearlybelow half the fiber diameter, preferably under 10% of the fiberdiameter.

A flame-retardant agent, which was subjected to an additionalpurification step with diluted acid, has proven to be particularly wellsuited to the lyocell process.

One highly suited process for the production of a flame-retardant agentfor use in cellulosic fibers comprises the following steps:

(a) Reaction of at least one tetrakis hydroxyalkyl phosphonium compoundwith at least one nitrogen compound, selected from the group of urea,thiourea, biuret, melamine, ethylene urea, guanidine and2-cyanoguanidine, to obtain a polymer whereby the molar ratio of thetetrakis hydroxymethyl phosphonium compound to the nitrogen compoundlies in the range of 1:(0.05 to 2.0), preferably in the range of 1:(0.5to 1.5) and most preferably in the range of 1: (0.65 to 1.2),

(a′) Cross-linking of the polymer obtained in process step (a) with thehelp of ammonia and

(b) Oxidation of the phosphorus contained in the cross-linked polymer asa result of adding an oxidation agent in order to obtain theflame-retardant agent.

The first step of the production process (a) and/or the steps (a) and(a′) serves respectively serve to produce a polymer by reacting the atleast one tetrakis hydroxyalkyl phosphonium compound with at least onenitrogen compound selected from the group of ammonia, urea, thiourea,biuret, melamine, ethylene urea, guanidine and 2-cyanoguanidine.

The hydroxyalkyl groups of the tetrakis hydroxyalkyl phosphoniumcompounds are hydroxymethyl, hydroxyethyl, hydroxypropyl or hydroxybutylgroups.

The at least one tetrakis hydroxyalkyl phosphonium compound, preferablyis a tetrakis hydroxymethyl phosphonium compound, hereinafter also named“THP”, with the general formula (P⁺(CH₂OH)₄)_(t)X⁻, or also the blendsof compounds of this kind whereby X⁻ stands for an anion and t for thevalence of this anion. t can thereby stand for a whole number of 1 or 2.For example sulphate, hydrogen sulphate, phosphate, mono or dihydrogenphosphate, acetate or halogen anions, such as fluoride, chloride andbromide, are suitable as anion X⁻.

With the at least one nitrogen compound, which is reacted in the processsteps (a) and (a′) with the tetrakis hydroxyalkyl phosphonium compound,meant one compound, two compounds, three compounds or several compoundsselected from the group of ammonia, urea, thiourea, biuret, melamine,ethylene urea, guanidine and 2-cyanoguanidine. In accordance with apreferred embodiment of the invention, the nitrogen compound is urea. Inaccordance with one particularly preferred embodiment of the invention,in process step (a) at least one nitrogen compound, selected from thegroup urea, thiourea, biuret, melamine, ethylene urea, guanidine and2-cyanoguanidine is reacted and the resulting polycondensation productis cross-linked with ammonia in a subsequent process step (a′).

The reaction (conversion) in process step (a) and as the case may bealso in process step (a′), is performed in a solvent in accordance withone preferred embodiment of the invention. The solvent preferably usedis water. The content of the at least two compounds to be converted inprocess step (a) respectively (a′) can vary across a wide range and ingeneral it equals 10 weight percent to 90 weight percent, preferably 20weight percent to 40% weight percent in relation to the overall mass ofthe reaction mixture used in process step (a) respectively (a′),containing at least the two compounds to be reacted and the solvent.

The molar ratio of the tetrakis hydroxyalkyl phosphonium compound to thenitrogen compound can vary across a wide range and generally lies in therange of 1:(0.05 to 2.0), preferably 1:(0.5 to 1.5), most preferably1:(0.65 to 1.2). As a result of deliberately selecting this molar ratio,it is ensured that the flame-retardant agent produced in accordance withthe invention does not dissolve or only dissolves to a limited extent inthe solvents used for the production of flame-retardant cellulosefibers.

The conversion in process step (a) and/or (a′) is generally preferred ata temperature in the range of 40 to 120° C., preferably at a temperaturein the range of 80 to 100° C. over a period of 1 to 10 hours andpreferably over a period of 2 to 6 hours.

In accordance with a general embodiment of the invention, followingprocess step (a), one can cool the reaction mixture which contains thepolymer to room temperature, i.e. to a temperature in the range ofaround 15 to 25° C., and preferably to a temperature of 20° C., prior tofurther cross-linking of the polymer in process step (a′) with ammonia.

In accordance with a preferred embodiment of the invention, one adds oneor several dispersing agents to the polymer after performing processstep (a) and prior to performing process step (a′), and thus prior tocarrying out cross-linking using ammonia. These dispersing agents arepreferably selected from the group of poly-vinylpyrrolidone,C₁₄-C₁₇-alkyl sulfonates, hydroxylpropyl cellulose (HPC) andpolyethylene glycol (PEG). The dispersing agent thereby serves tostabilise the components in the composition and prevents theagglomeration of polymers in the subsequent cross-linking reaction inprocess step (a′). Typically the at least one dispersion agent is in aconcentration in the range of 0.01 weight percent to 3 weight percent,preferably in the range of 0.1 weight percent to 1 weight percent, inrelation to the reaction mixture.

If the production of the polymer is performed in two stages, withprocess steps (a) and (a′), then ammonia is added in process step (a′)in a molar ratio to the tetrakis hydroxymethyl phosphonium compound inthe range of (1 to 4.0):1, preferably in the range of (1.2 to 3.5):1,most preferably in the range of (1.5 to 2.0):1. In this respect ammoniais added according to a preferred embodiment of the invention, until thereaction mixture reaches a pH-value in the range of 7 to 10, preferablyin the range of 8 to 9. In this way the polymer obtained in step (a) iscross-linked by means of ammonia in process step (a′) and a precursor ofthe flame-retardant agent is obtained, which is oxidized in thesubsequent step, process step (b). The duration of the conversion inprocess step (a′) generally lies in the range of 1 min. to 60 min.

The oxidation in process step (b) can be done with the help of the usualoxidation agents such as hydrogen peroxide, ammonium persulphate, air(oxygen) and perchloric acid. The molar ratio between the preliminarystage of the flame-retardant agent and the oxidation agent is generallyaround 1:1 to 1:1.2.

The flame-retardant agent obtained in process step (b) is washed with anacid in a subsequent process step (c) in accordance with a preferredembodiment of the invention. In this respect the flame-retardant agentcan be pre-purified, using common methods known to the specialist, forexample by means of filtration. The acid employed in process step (c) isgenerally selected from the group of HCl, H₂SO₄, H₃PO₄ and acetic acid.The acid is generally used in a concentration of around 1 to 75%,preferably in a concentration of around 1 to 20%, most preferably in aconcentration of around 1 to 9%, diluted in a solvent selected from thegroup of water, methanol, ethanol, N,N-dimethylformamide (DMF) andN-methyl morpholine oxide (NMMO) or a mixture of these. The solventgiven preference for diluting the acid is water. The quantity of acidused to wash the flame-retardant agent obtained in process step (b), canvary across a wide range. In general, one part by volume of acid perpart by volume of flame-retardant agent is used for washing. Accordingto one preferred embodiment of the invention two parts by volume areused and according to one specially preferred embodiment of theinvention, three parts by volume of acid are used for washing.

The flame-retardant agent obtained in process step (b) can subsequentlybe washed with an acid, as described before, and then washed with asolvent one or several times whereby one to two parts by volume ofsolvent, in relation to the volume of the flame-retardant agent, areused. For washing a solvent is preferably used which is selected fromthe group of water, methanol, ethanol, N,N-dimethylformamide (DMF),N-Methyl morpholine oxide (NMMO), or a mixture of these. Washing withwater is preferable.

The flame-retardant agent can now be subsequently separated from thesolvent used by means of a separation process, such as filtration. Ingeneral the remaining content of solvent then equals 0 to 40 weightpercent, preferably 0 to 20 weight percent and most preferably 0 to 10weight percent.

To improve the ability to be incorporated into fibers respectively fibermaterials, by way of example within the framework of the lyocell orviscose process, it is of advantage to grind the flame-retardant agentfor example in a ball, sand, glass pearl or a quartz pearl mill to anaverage particle size of 0.5 to 5 μm, preferably 1 μm. Grinding caneither be done by means of wet grinding or dry grinding.

PRODUCTION EXAMPLE 1

Production of a Product with a Mol Ratio of Urea to TetrakisHydroxylmethyl Phosponium Sulphate (THPS) of 1 to 0.77

66.2 kg of water, 10.5 kg of urea and 59.5 kg THPS (75% volumepercentage) are mixed and subsequently heated for a period of 3 hours at95 to 98° C. whilst being stirred. The reaction mixture is thereaftercooled down to a temperature below 30° C., 2.1 kg of Duralkan™ TL 844(PVP 25%) and 30 kg of ammonia (25 volume percentage) are introduced.Using ammonia, the pH-value is set at a value of around 8 and thereaction mixture is allowed to react for 1 min. Following this, 21.3 kgof hydrogen peroxide solution (30 volume percent) is introduced. Thesolid contained (flame-retardant agent) is separated via a drum filterat a temperature of 40° C., and finally washed with a quantity of waterequivalent to the volume of the solid. A white product is obtained witha solid matter content of 35 weight percent.

PRODUCTION EXAMPLE 2

Production of a Product with a Molar Ratio of Urea to THPS of 1 to 0.77

68 kg of water, 10.5 kg of urea and 59.5 kg THPS (75 volume percent) aremixed and subsequently stirred for a period of 5 hours at a temperatureof 95 to 98° C. The reaction mixture is then cooled down to atemperature below 30° C., 0.5 kg Hostapur™ SAS and 30 kg ammonia (25%volume percent) are subsequently added. Using ammonia, the pH-value ofthe reaction mixture is set at a value of 8 and the reaction mixture isleft to react for 1 min. Then 21.3 kg of hydrogen peroxide solution (30volume percentage) is introduced. The solid contained (flame-retardantagent) is separated at a temperature of 40° C. via a drum filter, washedwith a quantity of water equivalent in volume, then washed with aquantity of 3 volume percent hydrochloric acid equivalent in volume andfinally washed with a quantity of water at least equivalent in volume. Awhite product is obtained with a solid content of 35 weight percent.

The oxidized condensates which are produced in this way from a tetrakishydroxyalkyl phosphonium salt with a nitrogenous compound are suitableas a flame-retardant agent in a cellulosic moulded body.

Urea or ammonia are preferred as the nitrogenous compound.

The tetrakis hydroxyalkyl phosphonium compound is preferably a tetrakishydroxymethyl phosphonium salt.

The share of flame-retardant agent in the cellulosic man-made fiber, inthe form of a viscose or lyocell fiber, can be between 5 weight percentand 50 weight percent, preferably between 10 weight percent and 30weight percent, most preferably between 15 weight percent and 25 weightpercent in relation to the fiber. When the share is too low, theflame-retardant effect is insufficient, with shares above this limit,the mechanical properties of the fiber deteriorate excessively. Aflame-retardant cellulosic man-made fiber can be obtained with theseshares which is characterized by the fact that the tenacity in aconditioned state equals from 18 cN/tex to 50 cN/tex.

In addition, the flame-retardant cellulosic man-made fiber can containadditional additives, such as dyestuffs or bactericides.

In the final product (textile fabric), the cellulosic man-made fiber inaccordance with the invention fulfils the requirements according to ENISO 14 116 (previously EN 533) classification “limited flame spreadindex 3”, when testing in accordance with EN ISO 15025:2002 processB—edge flaming.

In the test procedure according to EN ISO 15025:2002, a defined flamefrom a stipulated burner is directed at the surface (process A) or thelower edge (process B) of vertically arranged textile samples for 10 s.The spreading of the flame and the afterglowing as well as the formationof particles dropping off and burning particles dropping off, are to berecorded.

The requirements in EN ISO 14 116 for the “limited flame index 3”, areas follows:

-   -   The flame is not allowed to reach the upper edge on any of the        test bodies    -   None of the test bodies should release burning particles    -   The afterglow should not spread from the carbonized part of the        test body to the undamaged part    -   The subsequent burning time must be below two seconds

A yarn can be spun from the fiber in accordance with the invention whichcan be further processed to a textile fabric. The fiber in accordancewith the invention can also be used to produce non-wovens.

The textile fabric resp. non-woven produced from the fiber in accordancewith the invention fulfilled the requirements of EN ISO 14 116classification “limited flame spread index 3”, when testing according toEN ISO 15025:2002 process B—edge flaming.

The yarn, textile fabric or nonwoven containing the flame-retardantcellulosic man-made fiber in accordance with the invention can beblended with fibers of natural or synthetic origin. The fibers ofnatural or synthetic origin can be either inherently flame-retardant orbe finished in this way. Examples of this are (flame-retardant)polyester, modacryl, para- and meta-polyaramide, polyamide-imide(Kermel®), (flame-retardant) wool, polybenzimidazol (PBI), polyimide(P84®), polyamide, (flame-retardant) polyamide, flame-retardant acrylicfibers, melamine fibers, polyphenylene sulphide (PPS),polytetrafluorethylene (PTFE), glass fibers, cotton, silk, carbonfibers, oxidized thermally stabilized polyacrylonitrile fibers (PANOX®)and electrically conductive fibers and blends of these fibers.

In particular para- and meta-polyaramide- and/or polyimide fibers areparticularly well suited for blending with the flame-retardant man-madefibers according to the invention.

The applicational purpose of the fiber in accordance with the inventionor fiber blends containing the fiber in accordance with the invention,is in all kinds of protective clothing such as e.g. fireman uniforms,protective clothing against contact with molten metals, underwear anduniform parts in the military sector, textile materials in the publicsector such as e.g. curtains and seat covers, textiles in means oftransportation such as e.g. airline seats, flame-retardant outer andintermediate sheets (fire blocker) consisting of a textile or non-wovenmaterial e.g. for mattresses.

EXAMPLE 1

A viscose with a composition of 6.0% cellulose/6.5% NaOH was made from abeech pulp (R18=97.5%) using 40% CS₂. To the viscose with a spinninggamma value of 62 and a viscosity of 120 falling ball seconds, amodifying agent (2% dimethylamine and 1% polyethylene glycol 2000,always in relation to cellulose) and 22% in relation to cellulose of theflame-retardant agent according Production example 1, in the form of a12 weight percent dispersion in 60 weight percent NMMO, were added. Themodified viscose was spun with 60 μm spinnerets into a spinning bathwith the composition 72 g/l sulphuric acid, 120 g/l sodium sulphate and60 g/l zinc sulphate with a temperature of 38° C., stretched to 120%inside a second bath (water with 95° C.) and finally drawn off at 42m/min. The after-treatment (hot dilutedH₂SO₄/water/desulphurizing/water/bleaching/water/finishing agent) wasperformed according to well known methods.

The dried fibers were processed to a yarn of Nm 30 and these were inturn processed to a knitted stocking with a mass per unit area of 200g/m², using a circular knitting machine.

The knitted stocking was subjected to the vertical flame test accordingto EN ISO 15025:2002 process B—edge flaming. The results of the flametest are shown in Table 3 and the fiber data in Table 1.

TABLE 1 Breaking Fiber Tensile strength elongation thickness conditionedconditioned Example [dtex] [cN/tex] [%] 1 2.17 20.1 12.3

EXAMPLE 2

22% in relation to cellulose of the flame-retardant agent according toproduction Example 1 in the form of a 12 weight percent dispersion in 60weight percent NMMO were added to the slurry (mixture of pulp/aqueousNMMO) and water was evaporated to yield a fiber-free spinning solutionwith the composition 12% cellulose/77% NMMO/11% water. A sulphate-highalpha pulp was used as pulp.

The spinning mass was spun to 2.2 dtex fibers, using the well-knownwet-dry spinning process with a spinning temperature of 110° C. with thehelp of a 100 μm spinneret into a spinning bath containing 25% NMMO witha temperature of 20° C. The washed and dried fibers were processed asdescribed in Example 1 to a knitted stocking and then subjected to thevertical flame test according to EN ISO 15025:2002 process B—edgeflaming. The results of this flame test are shown in Table 3 and thefiber data are shown in Table 2.

EXAMPLE 3

The same procedure was followed as in Example 2, however, aflame-retardant agent was used according to Production example 2. Theresults of the flame test can be found in Table 3 and the fiber data inTable 2.

TABLE 2 Yield Breaking Flame-retardant Tensile strength elongation agentconditioned conditioned Example [%] of input [cN/tex] [%] 2 95.1 34.113.4 3 99.3 34.3 11.6

TABLE 3 Burning behaviour according Phosphorus- to EN ISO 15025:2002content After-burning Degree of Example [%] time [s] destruction [mm] 12.1 0 186 2 2.2 0 69 3 2.5 0 7

The invention claimed is:
 1. A process for the production offlame-retardant cellulosic man-made fibers from a spinning masscomprising the following steps: (a) producing a viscose of cellulosexanthogenate from a pulp with an R-18 content of 93-98%, wherein theviscose has a cellulose content of between 4 and 7%, an alkali ratio ofbetween 0.7 and 1.5, and a carbon disulphide content of between 36 and42 weight percent in relation to cellulose; (b) adding between 1 and 5weight percent of a modification agent, in relation to cellulose; (c)adding 5 to 50 weight percent of a flame-retardant agent in relation tothe cellulose in the form of a aqueous dispersion of the flame retardantagent, wherein the flame retardant agent consists of an oxidizedcondensate of a tetrakis hydroxyalkyl phosphonium salt with ammonia; (d)spinning of spinning mass through a spinneret into a spinning bath,wherein the spinning mass has a spinning gamma value of between 50 and68 and a die spinning viscosity of between 50 and 120 falling ballseconds, wherein the spinning bath has a temperature of between 34 and48° C., wherein the spinning bath contains 68-90 g/l H₂SO₄, 90-160 g/lNa₂SO₄, and 30-65 g/l ZnSO₄; and wherein a final drawing-off from thespinning bath is performed at a speed of between 15 and 60 m/min; (e)stretching of precipitated filaments; (f) providing after-treatment viawashing, bleaching, and finishing; and (g) cutting to staple fibershaving a strength of more than 18 cN/tex in the conditioned state.
 2. Aprocess for the production of flame-retardant cellulosic man-made fiberscomprising adding a flame-retardant agent prior to extrusion of aspinning mass, wherein the flame-retardant agent consists of an oxidizedcondensate of a tetrakis hydroxyalkyl phosphonium salt with ammonia,wherein a share of flame-retardant agent in the cellulose fiber equals 5weight percent to 50 weight percent, wherein said fiber is producedaccording to a lyocell process, wherein said fiber has a strength ofmore than 18 cN/tex in the conditioned state.
 3. The process accordingto claim 2, wherein the flame-retardant agent is washed with acid andfinally with water in order to produce a dispersion thereof beforeadding the dispersion to the spinning mass.
 4. The process for theproduction of flame-retardant cellulosic man-made fibers according toclaim 1, wherein the spinning gamma value is between 55 and
 58. 5. Theprocess according to claim 2, wherein the share of flame-retardantsubstance in the cellulose fiber is between 10 and 30 weight percent. 6.The process according to claim 2, wherein the share of flame-retardantsubstance in the cellulose fiber is between 15 and 25 weight percent. 7.The process according to claim 1, wherein the flame-retardant agent iswashed with acid and finally with water before adding to the spinningmass before producing the dispersion thereof.
 8. A process for theproduction of flame-retardant cellulosic man-made fibers from a spinningmass comprising the following steps: (a) producing a viscose ofcellulose xanthogenate from a pulp with an R-18 content of 93-98%,wherein the viscose has a cellulose content of between 4 and 7%, analkali ratio of between 0.7 and 1.5, and a carbon disulphide content ofbetween 36 and 42 weight percent in relation to cellulose; (b) addingbetween 1 and 5 weight percent of a modification agent, in relation tocellulose; (c) adding 5 to 50 weight percent of a flame-retardant agentin relation to the cellulose in the form of a aqueous dispersion of theflame retardant agent, wherein the flame retardant agent consists of anoxidized condensate of a tetrakis hydroxyalkyl phosphonium salt withammonia and a nitrogenous compound which contains one or several groupsof amine groups; (d) spinning of spinning mass through a spinneret intoa spinning bath, wherein the spinning mass has a spinning gamma value ofbetween 50 and 68 and a die spinning viscosity of between 50 and 120falling ball seconds, wherein the spinning bath has a temperature ofbetween 34 and 48° C., wherein the spinning bath contains 68-90 g/lH₂SO₄, 90-160 g/l Na₂SO₄, and 30-65 g/l ZnSO₄; and wherein a finaldrawing-off from the spinning bath is performed at a speed of between 15and 60 m/min; (e) stretching of precipitated filaments; (f) providingafter-treatment via washing, bleaching, and finishing; and (g) cuttingto staple fibers having a strength of more than 18 cN/tex in theconditioned state.
 9. A process for the production of flame-retardantcellulosic man-made fibers comprising adding a flame-retardant agentprior to extrusion of a spinning mass, wherein the flame-retardant agentconsists of an oxidized condensate of a tetrakis hydroxyalkylphosphonium salt with ammonia and a nitrogenous compound which containsone or several groups of amine groups, wherein a share offlame-retardant agent in the cellulose fiber equals 5 weight percent to50 weight percent, wherein said fiber is produced according to a lyocellprocess, wherein said fiber has a strength of more than 18 cN/tex in theconditioned state.